He joined the USC staff in 1986. He coached WR Ken Henry to a season where he had 807 yards with 7 TD. WR Randy Tanner also had 408 yards with 3 TD.[1]

He then moved to the coaching staff at the University of California, Berkeley (Cal) in 1987. In 1987, WR Brian Bedford had 515 yards with 4 TD. WR Mike Ford had 479 yards with 3 TD.[2] In 1989, WR Brian Treggs had 746 yards with 4 TD.[3]

Mariucci's 1997 team went 13–3 during the regular season, earning home-field advantage in the National Football Conference (NFC). After defeating the Minnesota Vikings in the Divisional Playoffs, San Francisco hosted the Green Bay Packers in the NFC Championship Game, but lost 23–10 in a muddy, rainy contest at Candlestick Park. The defeat was the 49ers fourth NFC title loss of the 1990s, following losses to the New York Giants in 1990 and the Dallas Cowboys in 1992 and 1993. In 1998, the 49ers posted a 12–4 record and returned to the playoffs as a wild card team, but lost 20–18 in the divisional round to the eventual NFC champion Atlanta Falcons. Two losing seasons followed, but in 2001, the 49ers returned to the playoffs after a 12–4 season, once again to be eliminated by the Packers.

Mariucci's final season in San Francisco was 2002. The 49ers won the NFC West with a 10–6 record and beat the New York Giants in a controversial wild-card game, posting the third-biggest comeback playoff victory in NFL history (second biggest at the time). However, they were crushed 31–6 by the eventual Super Bowl champion Tampa Bay Buccaneers in the divisional round. On January 15, 2003, the 49ers fired Mariucci, reportedly after the coach lost a power struggle with general manager Terry Donahue.[6] As San Francisco's coach, he compiled a 60–43 (.583) record, while his teams earned playoff berths four times.

Mariucci was named the Lions' 22nd head coach on February 4, 2003, and was fired on November 28, 2005. In his 2+ years in Detroit, he compiled a disappointing 15–28 record. Mariucci's troubles in Detroit were partially attributed by many fans and experts to poor personnel evaluations by then Lions' General Manager Matt Millen, who had signed Mariucci to a five-year $25 million guaranteed contract, the NFL's highest coaching contract at the time. During his time in Detroit, the Lions never finished higher than third in their division and never contended for a playoff berth. The decision to fire Mariucci came after a 27–7 blowout loss on national television on Thanksgiving Day to the Atlanta Falcons.

During the Brett Favre–Green Bay Packers dispute throughout the 2008 off-season, Favre discredited the Packers for not interviewing Mariucci for their head coaching job in 2006. Mariucci, who previously worked with Favre, was figured to be a great candidate for the West Coast Offense style played in Green Bay.

Mariucci is one of thirteen head coaches since the AFL–NFL merger in 1970 to lead his team to a division title in his first season. Mariucci established an NFL mark for consecutive wins by a rookie head coach with an 11-game winning streak, which has since been trumped by Jim Caldwell's 14–0 start with the Indianapolis Colts during the 2009 season.

Since being fired by the Detroit Lions, Mariucci has not returned to coaching. He has since been hired by NFL Network to work on their show NFL GameDay and contribute as an analyst on NFL Network's four-hour pregame show "NFL GameDay Morning," as well as provide follow-up reports from the late afternoon and Sunday night matchups on "NFL GameDay Highlights."

Many speculated[who?] that Mariucci would be considered for the head coaching position at Michigan State after the dismissal of John L. Smith. However, Mark Dantonio was hired to replace Smith. Mariucci had been a prospective coach to replace Karl Dorrell at UCLA but such assertions[by whom?] were dismissed with the hiring of Ravens Offensive Coordinator and UCLA alumnus, Rick Neuheisel. He was also speculated to be in talks with the Washington Redskins, who have hired West Coast-style offense personnel since Joe Gibbs' second retirement.[9] However, the Redskins named former Seahawks' QB coach Jim Zorn as the head coach.[10]

Mariucci now resides in Monte Sereno, California. He has four children – Stephen, Tyler, Adam, and Brielle. Stephen and Adam are founders and frontmen to their pop-rock band The Relay Company.[11] His eldest son Tyler is an assistant athletic director at the University of Maryland.